1. Field of the Invention
The present invention relates to a semiconductor unit containing a semiconductor chip, and a semiconductor apparatus using the semiconductor unit.
2. Description of the Related Art
It is known, for example in Japanese Unexamined Patent Application Publication No. 2000-156439 (see FIG. 1), referred to herein as “Patent Document 1,” to construct a semiconductor module, in a package, containing power semiconductor elements such as an IGBT (an insulated gate bipolar transistor), a FWD (a free-wheeling diode) and the like mounted on an insulated substrate.
FIG. 17 is a sectional view of an essential part of a semiconductor module of a first conventional example. FIG. 17 shows a semiconductor module similar to that disclosed in Patent Document 1.
Referring to FIG. 17, an insulated substrate 55 is joined onto a cooling plate 54 with a solder or the like, and an IGBT chip 56 is mounted on the cooling plate 54 through the insulated substrate 55. A collector electrode 58 of the IGBT chip 56 is electrically connected to a metal thin plate 55a on the insulated substrate 55 with an electrically conductive material such as a solder or the like.
An external electrode terminal 62 for a collector is electrically connected to a metal thin plate 64b of a junction substrate 63b joined onto the cooling plate 54 with a solder or the like through a bus bar 60 for the collector. An aluminum wire 65 makes electrical connection between the collector electrode 58 of the IGBT chip 56 and the metal thin plate 64b of the junction substrate 63b. 
On the other hand, an external electrode terminal 61 for an emitter is electrically connected to a metal thin plate 55b of the insulated substrate 55 joined on the cooling plate 54 with a solder or the like, through a bus bar 59 for the emitter. A cooling member 67 of metal is joined to an emitter electrode 57 of the IGBT chip 56 through an electrically conductive junction member 66, and then, joined to a metal thin plate 64a of a junction substrate 63a with a solder or the like.
As a result, the emitter electrode 57 is electrically connected to the metal thin plate 64a of the junction substrate 63a through the cooling member 67, and then, electrically connected to the external electrode terminal 61 for the emitter through the bus bar 59 for the emitter. The reference numeral 68 represents a casing for containing the IGBT chip 56, and the reference numeral 69 represents silicone gel that seals off the contained members in the casing 68.
In this semiconductor module, the cooling member 67 composed of metal plates makes conjunction between the emitter electrode 57 on the upper surface of the IGBT chip 56 and the insulative junction substrate 63a disposed on the cooling plate 54. Consequently, the heat generated in the IGBT chip 56 is withdrawn from both upper and lower surfaces of the IGBT chip to the cooling plate 54.
Japanese Unexamined Patent Application Publication No. 2005-073373 (see FIG. 1), referred to herein as “Patent Document 2,” discloses a semiconductor module of a second conventional example used in a power conversion apparatus. This power conversion apparatus comprises: a semiconductor module containing semiconductor elements and having main electrode terminals and control electrode terminals; a control circuit board connected to the control terminal electrodes of the semiconductor module; a bus bar assembly composed of a plurality of bus bars connected to the main electrode terminals of the semiconductor modules; and a plurality of cooling tubes for cooling the semiconductor module from the both surfaces of the semiconductor module. The cooling structure for the semiconductor module of the power conversion apparatus has cooling bodies sandwiching the semiconductor module and cooling the semiconductor module from the both surfaces thereof.
In the first conventional example, the emitter electrode 57 on the upper surface of the IGBT chip 56 and the insulative junction substrate 63a provided on the cooling plate 54 are joined with the cooling member 67 composed of metal plates. The heat generated in the IGBT chip 56 is transported through the cooling member 67 and the insulative junction substrate 63a to the cooling plate 54. Consequently, a certain area is required as shown by the symbol ‘A’ in FIG. 18, for joining the cooling member 67 with the insulation junction substrate 63a (indicated in FIG. 17). This requirement for ensuring the heat transfer area raises a problem of increase in a module size.
An aluminum wire is used for connecting the collector electrode and the lead out terminal. The distance indicated by the arrow ‘B’ in FIG. 18 is required between the two places connected by the aluminum wire in order to avoid stress development in the wire and at the joints. This requirement for ensuring the distance raises a problem of increase in a module size.
A current density of the main current that runs in the aluminum wire can be hardly increased. In order to ensure sufficient magnitude of electric current capacity, the number of aluminum wires needs to be increased, which however, increases the number of wiring places of the wires and the number of manufacturing steps. In addition, need for reserving a region to connect a multiple of aluminum wires raises a problem of an enlarged module size.
Moreover, the apparatus is provided with a control pin block (not depicted in the figure) on a side wall surface of the casing, the control pin block being required for inputting control signals to control the IGBT chip 56. Need for an area to dispose the block makes minimization of the module difficult.
Patent Document 2 does not describe an internal structure of the semiconductor module. The semiconductor elements cannot be practically used without providing appropriate cooling bodies on the both surfaces of the semiconductor element. Thus, a power conversion apparatus, for example, a three phase inverter, using the semiconductor elements is enlarged.
Patent Document 1 and Patent Document 2 do not mention such a structure that a pair of electrically conductive plates sandwiches the semiconductor element from the both surfaces thereof and a leg portion of the electrically conductive plate bent in the shape of the letter ‘L’ is attached to a heat sink to cool the semiconductor element, and the structure is molded with a resin.